Electrophotographic developing apparatus using developing roller

ABSTRACT

An electrophotographic developing apparatus which supplies a developing solution to only one surface of the copy sheet which is to be developed, by using a developing roller, around the periphery of which are provided multiple threads having an optimum lead angle for the supply of the solution.

United States Patent 1 Sawada et al.

1 ELECT ROPHOTOGRAPHIC DEVELOPING APPARATUS USING DEVELOPING ROLLER [75] Inventors: Hideo Sawada, Sagamihara; Van

Hirafuji, Yokohama; Kenya Komada, Atsugi, all of Japan [73) Assignee: Ricoh Co., Ltd., Tokyo, Japan [22] Filed: Oct. 30, 1973 [21] Appl. No.: 410,988

[30] Foreign Application Priority Data Nov 13, 1972 Japan 47-113648 [52] US. Cl. 118/637; 118/D1G. 23; 117/37 LE [51] Int. Cl. G03G 15/10 [58] Field of Search 118/637, D10. 23, 258, 118/419, 423; 117/37 LE [56] References Cited UNITED STATES PATENTS 2,176,835 10/1939 Cumfcr 118/419 X [451 Sept. 16, 1975 3,179,536 4/1965 Martinek............. 118/637 UX 3,203,395 8/1965 Liller 1 18/637 X 3,245,381 4/1966 Brenneisen et al. l l8/DIG. 23 3,301,156 H1967 Roeber [IS/DIG 23 3,367,791 2/1968 118/637 X 3,384,051 5/1968 Hunstiger.. l18/DlG. 23 3,667,428 6/1972 Smith 118/016. 23

Primary ExaminerMervin Stein Arzorney, Agent, or Firm-Cooper, Dunham, Clark, Grifiin & Moran [57] ABSTRACT An electrophotographic developing apparatus which supplies a developing solution to only one surface of the copy sheet which is to be developed, by using a developing roller, around the periphery of which are provided multiple threads having an optimum lead angle for the supply of the solution.

4 Claims, 9 Drawing Figures PATEN M; 85? 1 5 mi;

SEEN 1 [1F 2 ELECTROPHOTOGRAPHIC DEVELOPING APPARATUS USING DEVELOPING ROLLER BACKGROUND OF THE INVENTION The invention relates to electrophotographic developing apparatus, and more particularly, & :2 wet devel oping apparatus using a roller in which developing solution is supplied to only one surface of the sheet to be developed through the action of the roller.

Both wet and dry developing means are known in electrophotography, that is, electrostatic photography and electrostatic recording. In the wet developing technique, the developing solution supplied to the surface of a sheet to be developed must be well stirred, since the developing solution serves as a carrier for a toner powder mixed therein, and unless the developing solution is well stirred, there cannot be achieved a uniform supply of toner powder to the surface to be developed, which results in a disadvantageous non-uniformity of developing. For this reason, the present applicant has previously proposed an apparatus for developing only one surface in which a developing solution is pumped by means of a roller around the periphery of which is formed a layer of developing solution, the surface to be developed of the sheet fed into the apparatus being caused to bear against such layer. In this manner, a stirring action is achieved through the pumping action of the developing solution. On the other hand, it is known that the greater the speed of relative movement between the developing solution and the surface to be developed, the better the developing effect which is achieved will be improved. This can be satisfactorily accomplished by the use of a developing process incorporating a roller.

The developing roller used in the developing solution of the kind described comprises either l a roller without a groove, (2) a roller with a simple groove or single thread groove, or (3) a roller having a plurality of grooves running parallel or substantially parallel to the axis of rotation. As a matter of practice, however, a developing apparatus incorporating such a developing roller failed to provide a smooth supply of the developing solution which is essential to the effectiveness of the roller developing technique. Specifically, the roller without groove under (I could not practically assure a smooth supply, while the roller under (2) resulted in a non-uniformity of developing in the direction of travel of the surface to be developed. Finally, the roller mentioned under (3), while improved over the first mentioned roller, cannot still achieve a completely smooth supply of the developing solution and is liable to induce developing nonuniformity on the surface to be developed in the direction of the axis of rotation.

SUMMARY OF THE INVENTION The present invention provides an electrophotographic developing apparatus using a roller in which the above-mentioned disadvantages are eliminated by forming on the periphery of the developing roller multiple threads having a suitable lead angle. In accordance with the invention, there is provided a developing appa ratus using a roller which eliminates the various disadvantages of the prior apparatus of this kind and capable of a smooth supply of developing solution to remove developing non-uniformity by forming on the developing roller multiple threads having a lead angle equal to or greater than Lm/v. 1)

As a further development of the invention, developing solution once used can be scraped off from the periphery of the developing roller by means of a cleaning member, thereby enabling fresh developing solution to be continuously supplied to the surface to be developed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic cross section of a developing apparatus using a roller in accordance with one embodiment of the present invention;

FIG. 2 is a top view illustrating the relative arrangement of the developing roller and the developing solution supply tank shown in FIG. 1;

FIG. 3 is a fragmentary enlarged view of the developing station;

FIG. 4 is a cross section, to an enlarged scale, taken along the line A-A of FIG. 2;

FIG. 5 is a cross section of developing apparatus using a roller in accordance with another embodiment of the invention;

FIG. 6 is a schematic cross section showing a modifcation of the apparatus according to the invention in which a cleaning member is added to the developing roller; and

FIGS. 7, 8 and 9 are views illustrating other examples of the cleaning member.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Referring to FIG. I, a sheet I to be developed having an electrostatic latent image formed thereon, as a result of exposure to radiation or by stylus recording, is fed, with its image surface located downside, by a pair of upper and lower feed rollers 20, 2b into a developing apparatus 3. The developing apparatus 3 comprises a developing solution supply tank 4; a developing roller 5 located adjacent to the tank 4, a pair of guide plates 70, 7b constraining the sheet 1 fed into the developing apparatus 3 so as to bring its lower surface, which is the surface to be developed, into contact with a layer of developing solution 60 to be formed on the upper periphery of the developing roller 5; another guide plate 9 for conveying the developed sheet toward a pair of upper and lower delivery rollers 80, 8b; and a reservoir 10 of developing solution disposed below the supply tank 4 and the developing roller 5.

The developing solution supply tank 4 is formed of a trough-shaped vessel and extends transversely to the direction of travel of the sheet 1, with its top and its side wall adjacent to the developing roller being open. A developing solution 6 contained in the reservoir 10 is pumped up into the supply tank 4 by means of a pump 11 and piping 12, both shown in phantom lines. The pumped developing solution is drawn out of the tank 4 by the rotating developing roller 5 to form a layer of developing solution 60 on the upper periphery thereof; the roller 5 being rotated clockwise, that is, in the direction of travel of the sheet I to be developed, with a peripheral speed V which is from two to four times the feed rate V of the sheet 1. As shown in FIG. 3, the surface lu to be developed of the sheet I fed into the apparatus is brought into contact with the layer of developing solution 6a thus formed for the purpose of developing by the developing solution 6.

In the arrangement shown, it will be appreciated that by denoting the effective length of the developing station by L; the distance through which a point on the sheet I traverses the region of effective length of the developing station by 1,; and the length of travel measured along the periphery of the developing roller 5 of a point thereon which passes through the long on the sheet 1, while the latter traverses the effective length of the developing station, by 1 the following relationship applies:

Thus 1 is proportional to the peripheral speed V of the roller 5.

The developing roller 5 which draws the developing solution 6 from the supply tank 4 is formed of a material such as aluminium, stainless steel of the like, and is positioned partly received within the open side wall of the supply tank 4 as shown in FIGS. 1 and 2, with its shaft 50 being connected with a drive source, not shown, to be driven for clockwise rotation as indicated by an arrow in FIG. 1.

Multiple threads are formed in the periphery of the developing roller 5. The multiple threads 5b have a lead angle a which is defined as:

01=tan (2) Substitution from equation (1) yields:

tan tan a 2 tan U I'U 2/ is found to be extremely useful.

The passage of thread grooves having a suitable lead angle 0: across the surface 1a to be developed in a chronologically concurrent manner while the sheet 1 traverses the region of the effective length of the developing station L assures a developing action which is free from developing non-uniformity on the developed surface la.

Thus, with the developing apparatus of the invention, thread grooves, having a suitable lead angle a carry the developing solution to the surface to be developed in a region from its supply side across the effective area for development is maintained covered with a fresh supply of developing solution. This can be best understood when compared against the prior art in which a roller without a groove or a developing roller having grooves running parallel to the axis of rotation is used to cause the formation in the area of contact between the sheet to be developed and the film of developing solution on the roller, from a sump of used developing solution or non-uniform distribution of fresh and used developing solutions, which prevents a supply of fresh developing solution from being maintained. By contrast, in accordance with the invention, a supply of fresh developing solution 6 is maintained across the surface In to be developed of the sheet 1 for the purpose of developing.

The developed sheet is conveyed on the guide plate 9 and discharged externally of the apparatus by means of the delivery rollers 8a, 8b. At the same time, the developing solution 6 which has been drawn out of the supply tank 4 by the developing roller 5 falls downwardly with the rotation of the roller, subsequent to the formation of the layer of developing solution 6a on the upper periphery thereof, and is received into the reservoir 10.

In one embodiment of the developing roller 5, the roller has an outer diameter of about 25 mm and is formed with multiple thread grooves 5b which comprise l 10 threads with a lead length of 132 mm and a pitch (width of groove) of 1.2 mm and with the angle of thread of 60. In this embodiment, the lead angle amounts to about 60, and when the ratio of V to V is chosen to be a value in a range from 2 to 4, the effective length L of the developing station becomes nearly 3 to 5 mm. In this instance, the normal circular pitch or the pitch determined in the AA plane shown in FIG. 2, of the multiple thread grooves 5b has a value of 0.6 mm (FIG. 4). Experiments have shown that the optimum results are obtained with a lead angle a of from 45 to 60 with V /V 2 to 4.

Preferably, the direction in which the developing roller 5 is rotated is chosen coincident with the direction of travel of the sheet to be developed, as indicated by an arrow b in FIG. 2.

FIG. 5 shows another embodiment of the invention. Referring to this FIGURE, the sheet 1 to be developed is fed, with its image surface located down side, by a pair of upper and lower feed rollers 20, 2b, and guided by a guide plate 16 into a developing apparatus 13. The developing apparatus 13 comprises a developing solution supply tank 14, a developing roller 5 located adjacent to the tank 14, and an upper guide plate 17 which constrains the sheet 1 fed into the apparatus so as to bring its lower surface or the surface to be developed into contact with the developing solution.

The developing solution supply tank 14 is in the form of a trough-shaped vessel and extends in a direction perpendicular to the direction of travel of the sheet I, with its top being open and covered by an apertured plate 18. The apertured plate 18 is formed with a multiplicity of small apertures 18a having a diameter on the order of 1 mm, with a density of ID to 30 per square centimeter. In the present example, the density is chosen as 25 per square centimeter. The supply tank 14 is supplied with a developing solution from a reservoir 10 of developing solution by means of a pump 1 l, and the developing solution supplied by the pump 11 fills the supply tank 14 and is caused to flood through the apertures 18a in the apertured plate 18 to the top thereof. Located adjacent to the supply tank 14 is a developing roller 5, similar to the one described above, which is formed with multiple threads 5b having a suitable lead angle a The roller 5 is rotated in the direction of an arrow u at a higher speed, for example, 2.5 times higher than the feed rate of the sheet I fed into the developing apparatus 13. A delivery roller 19 is disposed beyond the roller 5 as viewed in the direction of travel of the sheet 1. The guide plate 17 is positioned to cover the supply tank 14, developing roller and dclivery roller 19, and is formed with :1 depending portion 17(- which extends downwardly toward the supply tank 14 and another depcnding'portion 17d which extends downwardly'toward the space between the developing 5 roller 5 and the delivery roller 19. These depending portions 17c and 17d serve to press down the rear surface of the sheet so as to bring its surface to developedinto Contact with the developing so lgtion. r

In operation, as the developing solutiori is supplied from the reservoir to the. Supply tank 14 by means of the pump 11, the developing solution 6 fills the tank 14 and is caused to flood through the apertures 18a to the upper side of thelaperiured plate IBwThisfloOding deyeloping solution isdrawn by thevperiphery of the de-- veloping roller 5 which is rotating at a high speed to, form a layer of developing solution 6a on the periphery thereof. Tl'ie developing solution after cont aqting sheet 1 falls down the periphery of the roller- 5 and is collcct'ed in the rese i'voir It). the developing solution 6 is subjected to circulation along a path comprising" the reservoir [0, pump 11, supply tank 14, small apertures [8a. the periphery of the developing roller 5 and back to the reservoir 10. The developing solution is sufficiently stirred when it is supplied into the supply tank 14 by the pump 1]. When the sheet 1 is fed with its image surface disposed downwardly, into the developing apparatus 13. the upper surface of the leading edge of the sheet is initially constrained by the depending portion 17c to thereby bring the surface to be developed of the sheet I into contact with the developing solution which has flooded through the small apertures 180, the leading edge is then fed toward the developing roller 5. Subsequently, the surface to be developed moves into contact with the layer of developing solution 6a formed on the periphery of the developing roller 5, and after passing thercover is fed toward the delivery roller 19. During this process. the developing solution is supplied to only one surface of the sheet that is, the surface to be developed As the sheet 1 approaches the delivery roller 19, the depending portion [7d of guide plate 17 prevents it from lifting up, so that the sheet 1 assumes a suitable configuration in which it is pressed down by the depending portions 170 and 17d during the time of travel through the apparatus with its surface to be developed maintained in contact with the layer of developing solution 6a formed on top of the developing roller as well as with the body of the developing solution which has flooded through the aperturcd plate 18. After passing over the delivery roller 19, the developed sheet is discharged externally of the apparatus by a pair of upper and lower discharge rollers 81:. 8b.

With the above arrangement of the developing apparatus, the developing roller 5 is forced to rotate with a peripheral speed which is several times the feed rate of the sheet I, while the developing solution moves at substantially the same speed as the feed rate of the sheet 1. The arrangement is such that the developing solution once supplied to the surface la to be developed of the sheet 1 falls off the developing roller 5 as it rotates and is collected by the reservoir [0. However, because of the high speed with which the developing roller 5 rotates, a portion 6b (see FIGS 1 and 6) of the used developing solution or which should normally drop into the reservoir 10 tends to continue rotating with the dcveloping roller without being released from the periphcry thereof thus undergoing acirculation around the periphery of the roller 5. Such circulation results in a reduced toner concentration in the developing solution supplied to the surface' la to be developed. since it has once been used in the developin gprocess before being brought into contact with the surface to be developed. While such circulation is undesirable, it is similarly undesirable when the developing solution mixed with a tonerpowder isin a still condition since a sufficient de veloping effect cannot be achieved for the later half of the sheet because the amount of toner in the developing solution placed in contact with the latent image becomes insufficient for the later half.

Such disadvantageous reductions in the toner concentration are avoidedbythe use of a cleaning member in the apparatusof the invention as shown in FIG. 6. Referring to :this Figure, the developing apparatus shown comprises a developing solution supply tank 24 which iscovered at its top by an apertured plate 18 and has an open side adjacent to the developing roller 5, the roller 5 being partly received in the tank-24; That portion 6b of the'used developing solution which remains attached to the periphery of the roller 5 is scraped off by a cleaning member 20 which is located within the supply tank 24. The cleaning member 20 comprises a brush and its base 20a is retained within a support 24b which is formed such as by folding the bottom plate 24a of the tank 24 into a U-shaped cross section. The free end of the cleaning member 20 extends into the developing solution 6 within the supply tank 24, and its forward end abuts against the periphery of the developing roller 5 in the interior of the supply tank 24. The portion 6b of the used developing solution which goes around the periphery of the developing roller 5 can be scraped off by the forward end 20b of the brush or cleaning member 20 before it reaches the layer of developing solution 6a formed on top of the developing roller 5, whereby the roller periphery is cleaned. As a consequence, the layer 6a on the roller periphery is formed by a supply of fresh developing solution which passes over the forward end 20b of the brush and through the apertured plate 18.

FIG. 7 shows another embodiment of the cleaning member 20 which comprises a film 20A of polyester such as Mylar (registered trademark) or the like. The base 20Aa is mounted on a suitable support member 24b, and the forward end 20Ab is held in abutment against the periphery of the developing roller 5. It is desirable that the forward end 20Ab of the cleaning member 200 be formed with a number of cuts 20Ac just in the manner of a brush, as shown in FIG. 8, in order to ensure its abutment against the periphery of the developing roller which is provided with thread grooves 5b for the purpose of drawing the developing solution.

While in the above examples, the cleaning member 20, 20A is disposed within the supply tank 24, it may be located immediately beyond the point at which the developing solution falls off the roller periphery, as viewed in the direction of rotation of the roller,

Alternatively, the forward end 20Ab (20b) of the cleaning member 20A (20) may be held abutting against the developing roller 5 in a direction opposite to the direction of rotation thereof, as shown in FIG. 9. Specifically, the base 20Au (20a) of the cleaning member 20A (20) is mounted on the outside of the bottom plate 24a of the supply tank 24, and its forward end 20Ab (20b) may be held in abutment against the periphery of the developing roller in a direction opposite to the direction of rotation of the roller. In this manner, the used developing solution can be scraped off by the cleaning member, thereby enabling a supply of fresh developing solution to be maintained against the surface to be developed.

What isyclaimed is:

l. A developing apparatus for use at the developing station in wet-type electrophotographic copying machines comprising:

a. a tank for holding and supplying a developing solution; and

b. a developing roller means, disposed at the developing station and adjacent said tank with the peripheral surface thereof forming at least a part of a wall of said tank, for receiving developing solution from said tank on its peripheral surface and transferring it to the surface of a sheet fed thereby, said roller means rotating at a peripheral speed greater than the speed at which a sheet to be developed is fed thereby, and said peripheral surface of said roller means being formed with a series of threads having a lead angle a in accordance with the relationship:

where L is the efl'ective length of the developing station, b is the thread pitch, V, is the speed at which a sheet to be developed is fed by said roller means, and V is the peripheral speed of said roller means.

2. Apparatus as in claim 1 wherein said lead angle a is less than 2 tan 

1. A developing apparatus for use at the developing station in wet-type electrophotographic copying machines comprising: a. a tank for holding and supplying a developing solution; and b. a developing roller means, disposed at the developing station and adjacent said tank with the peripheral surface thereof forming at least a part of a wall of said tank, for receiving developing solution from said tank on its peripheral surface and transferring it to the surface of a sheet fed thereby, said roller means rotating at a peripheral speed greater than the speed at which a sheet to be developed is fed thereby, and said peripheral surface of said roller means being formed with a series of threads having a lead angle Alpha in accordance with the relationship:
 2. Apparatus as in claim 1 wherein said lead angle Alpha is less than 2 tan 1
 3. Apparatus as in claim 1 wherein said lead angle Alpha is in the range from 45* to 60* and V2/V1 is in the range from 2 to
 4. 4. Apparatus as in claim 1 further comprising a cleaning member abutting aGainst the peripheral surface of said developing roller means at a point in the rotation of said developing roller means subsequent to its passing through said developing station. 